In recent years, mobile communications devices for both voice telephone services and data services such as email or text messaging or even multi-media services has become commonplace among mobile professionals and throughout the more general consumer population. Simultaneous mobile voice and data services have become virtually ubiquitous across much of the world. This is shown in FIG. 1, which is a functional block diagram of an exemplary system 100 of networks for providing mobile voice telephone services and various data services. For discussion purposes, diagram 100 shows two wireless networks 120 and 135 operated in accordance with, e.g., different technology standards. The networks 120 and 135 may be operated by different providers, carriers or operators. The communication networks 120 and 135 provide mobile voice telephone communications as well as other data services for numerous mobile stations.
The system 100 also includes mobile devices such as 105 and 125, typically operated by the networks' customers. Today, mobile devices typically take the form portable handsets, smart-phones personal digital assistants, or data cards for computers, although they may be implemented in other form factors. Each mobile communication network 120 or 135 provides communications between mobile stations 105 and 125 as well as communications for the mobile devices with other networks and stations outside the mobile communication networks. An inter-carrier or other intermediate network 140 may provide communication connectivity between the mobile communication networks 120 and 135. An example of such an intermediate network is a Public Switched Telephone Network (PSTN).
Each network 120 and 135 allows users of the mobile stations operating through the respective network to initiate and receive telephone calls or data to each other as well as through the public switched telephone network (PSTN) 140 connected thereto. One or both of the networks typically offers a variety of text and other data services, including services via the Internet 145, such as downloads, web browsing, e-mail, etc. via servers shown generally at 150 as well as message communications with terminal devices represented generally by the personal computer 160. To initiate a call, a user of a mobile device, e.g., 105, may communicate with one or more base stations, e.g., 110, . . . , 115 in a particular network, e.g., 120, in order to reach an intended receiver, e.g., 125. Similarly, to receive data from, e.g., a web server, a mobile device, e.g., 105 may connect with a base station in the locale where the mobile device is situated and via network 135 to connect to a server, e.g., 150 on the Internet. Mobile device 105 may be supported to perform communication with both mobile device 125 and server 150 simultaneously.
Radio access technologies for cellular mobile networks are continuously evolving to meet the future demands for higher data rates, improved coverage and capacity. The 3G Long Term Evolution (LTE) concept supports fast scheduling and link adaptation in frequency and time domains both for the uplink (UL) and the downlink (DL). This means that the resource assignment can be adjusted to the users' momentary traffic demand and channel variations. This includes the adaptation as to transmission power used by a mobile device to transmit signals based on the real-time situations. In general, excessive power usage should be avoided to save user equipment (UE) battery life and to avoid both intra-cell and inter-cell interference. The LTE specifications support a base station mechanism for controlling the transmit power of a mobile device or a user equipment (UE).
Typically, the Signal-to-Noise Ratio (SNR) or Signal-to-Noise and Interference Ratio (SINR) (when interference is accounted for) of the signals exchanged between a UE and a base station is controlled to stay below a targeted value SNRtarget. The UE power usage can be dynamically adjusted based on a variety of factors. For instance, it may depend on the scheduled bandwidth for transmission. For example, the UE power needs to be shared over the allocated bandwidth (BW). In a poor radio condition, a UE may not reach the targeted SNR even with a small bandwidth allocation. In a good radio condition, the UE power may be sufficient to fill the entire available bandwidth and still reach the target SNR. For a UE in intermediate radio condition the power may be sufficient up-to a certain bandwidth. In some situations, a UE may transmit with the maximum available power and the received SNR may depend on the momentary link path gain. The power used for a UE to transmit may also depend on the path loss of a particular locale.
To ensure optimal transmission quality, link adaptation is frequently employed. Such adaptation function estimates the transmission parameters (modulation and coding) based on an estimated SNR (or SINR if interference is estimated). For example, a LTE base station usually estimates the radio propagation condition, i.e. the path gain to determine the received SNR for a certain BW allocation. To do an efficient link adaptation and scheduling, a base station needs knowledge of the uplink gain of the user. To estimate the uplink condition, the base station should know both the received power from the UE and the transmit power used by the UE. While the base station can determine the received power by measurement on the uplink transmission, the UE transmit power is commonly made known to a base station via a power headroom report from the UE that reports the transmit power to the base station. In 3GPP, a UE measures power headroom and likely also reports the power headroom. The content may be the difference, e.g., between UE maximum power and UE transmit power, either a total value or a value per resource block, or the UE transmit power, either a total value or a value per resource block. The setting of the user equipment (UE) transmit power, PPUSCH, for the physical uplink shared channel (PUSCH) transmission in subframe i is defined by:PH(i)=PCMAX−{10*log10(MPUSCH(i))+PO—PUSCH(j)+α(j)*PL+ΔTF(i)+f(i)}[dBm]  (1)where, PH(i) is the power headroom computed at moment i. PCMAX is the configured maximum UE output power. The following parameters determine the value of Pcmax: the UE power class, maximum allowed power configured by higher layer and UE's implementation margins. The expression inside the braces corresponds to the power that is used for transmission determined based on different considerations. Therefore, PH(i) aims to provide a measurement for the unused power. The actual power used for transmission depends on dynamic field situations. For instance, MPUSCH(i) is the bandwidth of the PUSCH transmission expressed in number of resource blocks taken from the resource allocation valid for uplink subframe i from a scheduling grant received on subframe i-KPUSCH. PO—PUSCH is a parameter with 1 dB resolution composed of the sum of an 8-bit cell specific nominal component PO—NOMINAL—PUSCH signaled via broadcast control channel (BCCH) on the physical downlink shared channel (PDSCH) in the range of [−126,24] dBm and a 4-bit UE specific component PO—UE—PUSCH signaled via radio resource control (RRC) in the range of [−8, 7] dB. α has possible values {0, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1} and either is signaled by a 3-bit cell specific parameter via BCCH on the PDSCH, or has constant value of 1. PL is the downlink path loss estimate calculated in the UE from a reference symbol received power (RSRP) measurement and signaled reference symbol (RS) transmit power. ΔTF corresponds to a measure associated with the power used when a certain modulation is used. Item f(i) is related to the amount of increase in the signal strength determined dynamically by the network.
In a conventional user equipment (UE), the power headroom reporting is configured to be carried out when certain conditions are met. One typical power headroom reporting procedure is shown in FIG. 2, which dictates that a power headroom reporting occurs whenever (1) a periodic timer in accordance with a set period goes off, (2) the path loss is greater than a pre-determined threshold, and (3) a power headroom report is triggered by upper layer. Conditions to trigger power headroom reporting are often configured at an upper layer. When the condition is met, the PH(i) values as computed based on formula (1) are used to generate a power headroom report and are transmitted.
Specifically, the path loss is measured at 210. If the change in pass loss (ΔP) is greater than a pre-determined threshold, tested at 240, power headroom is to be reported at 270. The reported power headroom is computed based on the formulation as specified at 280. In addition to this power headroom reporting condition, there may be others as well. For instance, the power headroom reporting can be set up to be performed periodically. In this case, a power headroom reporting (PHR) tinier is checked, at 220, periodically and if the timer is expired, determined at 250, power headroom is to be reported at 270 in accordance with the computation as set forth at 280. In some situations, power headroom reporting may also be required. For example, upper layer configuration may be checked at 230. If it is required to perform power headroom reporting, determined at 260, power headroom is computed in accordance with the formula as set at 280 and reported at 270.
As discussed herein, more UEs are now capable of simultaneous multiple radio transmissions. As a result, a UE's actual maximum transmission power may vary dynamically. For example, when a UE conducts multiple radio transmissions simultaneously for, e.g., both voice and data transmission, the actual maximum power available for the LTE network may vary and may sometimes be smaller than PCMAX. However, the traditional power headroom computation, as illustrated in formula (1) and reporting triggering mechanism, as shown in FIG. 2, do not take into account such factors and, thus, will no longer work well. Therefore, a method and a system for power headroom computation and reporting thereof for UEs supporting simultaneous multiple radio transmissions are needed.